The purpose of this project is to further our understanding of the mechanism by which specific neuronotrophic factors induce and maintain a differentiated state in undifferentiated mammalian neuroblasts. To date, this project has dealt exclusively with one neuronotrophic factor, the nerve growth factor (NGF), known to be necessary for the development and maintenance of vertebrate sympathetic and sensory neurons. NGF is a multimeric protein made up of three dissimilar subunits, only one of which is biologically active. NGF of exocrine gland origin has been isolated and well characterized from mouse submaxillary gland and snake venom. More recently, NGF from guinea pig prostrate and human placenta at term has been isolated while its complete characterization is still under way. A large number of studies would suggest that there are alterations in ambient levels of NGF in humans suffering from a number of neuropathies involving the peripheral and central nervous system. However, there are inconsistencies in some of these report, difficulty in repeating some of the observations, as well as disagreement as to their significance. This is due in part to our ignorance of the regulatory mechanisms responsible for NGF synthesis, delivery and mode of action. These ambiguities also stem in part from: the use of murine-NGF as an antigen and standard iun assays on human tissues; the use of transformed rat non-neuronal adrenal clonal lines or of heterogenous cell populations in primary cultures in the study of NGF effects. In order to circumvent some of these problems, we propose to study the quarternary structure of NGF of human origin; synthesis of NGF by a murine sarcoma line (S180) and primary human fibroblast; effects of NGF on human neuroblastoma clonal lines (SK-N-SH-SY5Y and KA-9). Also, effects of NGF on 6-hydroxydopamine mediated cytotoxic effects will be investigated.